Optical cube



FIG. 1 is a left side perspective view of an optical cube in accordance with the new design;

FIG. 2 is a right side elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevation view thereof; and,

FIG. 6 is a rear elevation view thereof.

The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design. 

The ornamental design for an optical cube, as shown and described. 